When Air China Flight CA910 touched down at the Chinese city of Nanjing on 10 July, it was carrying more than just a planeload of passengers.
One of those people travelling from Moscow had the Delta variant of COVID-19. After they left the plane, staff from the Nanjing Lukou airport swooped in to pick up their rubbish.
According to Chinese officials, when those cleaners exited the aircraft they brought the virus along with them to the outside world - sparking what has now become China's widest outbreak since Wuhan.
In the last few weeks, at the height of the summer travel season, Delta has been detected in at least 16 Chinese provinces and municipalities. Most cases are linked to Nanjing.
Though there are a few hundred cases - relatively low for a country of 1.4 billion people - many are unnerved that the virus has appeared in major cities including Beijing, Shanghai and Wuhan.
In response, China has fallen back on familiar methods. Millions have been tested, sometimes more than once. Cities have gone into lockdown, while transport links in some areas have been cut.
It's what experts call a zero-tolerance or elimination strategy, seen not just in China but also other places such as Australia, New Zealand and Singapore.
But the astonishing speed of Delta's spread has also prompted questions about whether the approach is truly sustainable in China, in the face of a more transmissible COVID variant.